Method and device for forming a workpiece

ABSTRACT

A device ( 1 ) for forming a hollow and at least essentially rotation-symmetric workpiece ( 4 ), having an inner forming tool ( 3 ) for supporting an inner contour of the workpiece ( 4 ) and an outer forming tool ( 2 ) for introducing a forming force into an outer contour ( 10 ) of the workpiece ( 4 ). The workpiece ( 4 ) can be rotated relative to the outer forming tool ( 2 ) around an axis of rotation (X). The device ( 1 ) has a machining tool ( 15 ) and is designed such that the machining tool ( 15 ) can act upon the outer contour ( 10 ) of the workpiece ( 4 ) at the same time as the forming tool ( 2 ) in order to insure that the diameter of the workpiece ( 4 ) is uniform before the workpiece ( 4 ) is acted upon by the forming tool ( 2 ) to prevent whip arm or curvature in the workpiece ( 4 ).

TECHNICAL FIELD

The invention relates to a method and a device for forming a hollow andessentially rotation-symmetric workpiece.

BACKGROUND INFORMATION

Methods of the type in question are known from the prior art and arethere referred to as pressure rolling method. It is regularly theobjective of this method to form an essentially rotation-symmetrichollow piece, for example, a tube shaped hollow piece, wherein itsdiameter and its wall thickness decrease due to the plastic deformation.Due to the decrease in diameter and wall thickness, the length of thehollow piece regularly increases along a rotation-symmetric axis, i.e.,in axial direction. This enables the forming of hollow-shaped workpiecein methods and devices of the type in question in that a forming toolacts on the outer contour of the workpiece, while the workpiece rotatesaround an axis of rotation, which corresponds to the rotation-symmetricaxis of the workpiece within the scope of the manufacturing tolerancesof the workpiece. Due to plastic deformation, the material of theworkpiece is first displaced through the outer forming tools onto theinner forming tool, until the movement of the material is restrained bythe inner forming tool.

As a result, a plastic material flow occurs with three movementcomponents, namely an axial, i.e., oriented parallel to the axis ofrotation, a radial, i.e., directed toward the axis of rotation movementcomponent of the flowing material, and one directed perpendicular tothese two direction components in the circumferential direction. Theworkpiece elongates during plastic forming due to the axial movementcomponent.

The disadvantage of such forming methods is that there are high demandson the uniformity of the wall thickness of the used workpiece in thecircumferential direction. A so-called whip arm effect as shown in FIG.1 occurs if the wall thickness of the materials to be processed is tooirregular in the direction of the circumference. The formed workpiecewarps so that its centerline deviates from the axis of rotation andassumes a curved course. This leads to an imbalance that regularlyforces the termination of the process.

The occurrence of this so-called whip arm effect when processingworkpieces that have great wall thickness irregularities in thedirection of the circumference is thus far an unsolved problem for themethods in question.

Even with modified devices that have additional forming tools, forexample, as shown in FIG. 2, carrying out the forming methods inquestion is not successful if the requirement on the uniformity of thewall thickness in the direction of the circumference is not met by theworkpieces to be formed.

SUMMARY

The problem addressed by the invention is therefore to demonstrate amethod and device of the type in question that allows for processing ofworkpieces with greater irregularities in the wall thickness than is thecase according to the prior art.

The method according to the invention provides for a machining processof an area of the workpiece still to be formed during the formingprocedure. The device according to the invention is designed accordinglysuch that a machining tool of the device can act upon the outer contourof the workpiece at the same time as the forming tool.

It has been shown that the undesired, so-called whip arm effect is basedon the fact that an irregular wall thickness of the workpiece to beformed in the direction of the circumference leads to an increasedmaterial flow in the axial direction in the area of the greatest wallthickness and thus to an increased elongation in the respective area ofthe workpiece during forming. Although a material flow in thecircumferential area is also generated in the direction of thecircumference, when the irregularities in the wall thickness become toogreat, this may no longer be sufficient to bring about an equaldistribution of the material around the circumference during forming.The respective surplus material in the gap-like forming zone betweenouter and inner forming tools can then only evade the forming pressurein the axial direction, which leads to the already described buckling ofthe formed workpiece.

The outer forming tool, which is preferably a forming roll, is arrangedin the axial direction, preferably in the end zone of the inner formingtool. Advantageously, this inner forming tool can be designed as aninner mandrel around which the workpiece to be formed is arranged at thebeginning of forming. The preferably free end of the mandrel preferablyforms the counter support for the forming process, i.e., it provides thesurface against which the inner contour of the workpiece to be formed ispressed during forming.

Preferably, when carrying out the method according to the invention, afirst partial area of the workpiece in the axial direction is initiallyformed by using a machine tool to make the workpiece circumferenceuniform in size, preferably in the end section such that the formedpartial section comes to rest against the inner forming tool. Thisdefines the position of this end zone of the workpiece to be formedrelative to the inner forming tool and the area of the workpiece that isformed in this manner will be able to better absorb the reaction forcesthat arise during the following beginning machining action and introducethem into the forming tools.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features and advantages of the present invention will bebetter understood by reading the following detailed description, takentogether with the drawings herein:

FIG. 1—shows a schematic presentation of a forming method according tothe prior art;

FIG. 2—shows a schematic sectional presentation of a forming deviceaccording to the prior art; and

FIG. 3—shows a schematic sectional presentation of an exemplary deviceaccording to the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The device 1 according to the invention, like the presented device 1,FIG. 1 according to the prior art, has at least one outer forming tool 2and one inner forming tool 3. The shown exemplary outer forming tools 2are in advantageous fashion designed as forming rolls. In the shownexample, the inner forming tool 3 is designed as an inner mandrel. Thehollow-shaped, essentially rotation-symmetric shape of the workpiece,which in the shown example is advantageously pipe-shaped, allows for theworkpiece 4 to be formed to be arranged around the inner forming tool atthe beginning of forming.

When carrying out the forming method, the workpiece 4 to be formed ismade to rotate around the axis of rotation X relative to the outerforming tool 2. Through the movement of the workpiece 4 to be formed inthe feeding direction 5, the workpiece 4 to be formed is pressed throughbetween the outer forming tool 2 and the inner forming tool 3. Thesuperimposition of the feeding movement 5 and the rotation around theaxis X results in a helical track that the forming tool 2 followsrelative to the workpiece 4 to be formed.

Forming causes the length of the formed workpiece 6 to be elongatedcompared to the workpiece 4 to be formed.

In the shown example, a first wall thickness 7 of the workpiece 4 to beformed is greater than the second wall thickness 8 of the workpiece 4 tobe formed, wherein the areas with the first wall thickness 7 and thesecond wall thickness 8 are offset to each other in the direction of thecircumference.

The differences between the wall thicknesses 7 and 8 lead to aneccentricity of the workpiece 4 to be formed, which leads to thecenterline 9 of the outer contour 10 of the workpiece 4 to be formed notto coincide with the axis of rotation X. With the known method, the whiparm effect shown in FIG. 1 occurs during forming with the center line 11of the formed workpiece 6 assuming a curved course because the length 12of the formed area with the first wall thickness 7 is greater than thelength 13 of the formed area with the second wall thickness 8. Thiseffect occurs stronger as the centerline 9 of the outer contour 10 ofthe workpiece 4 to be formed deviates from the axis of rotation X asshown in FIGS. 2 and 3 by the distance 14.

The device according to the invention has a machining tool 15, FIG. 3,that acts upon the outer contour of the workpiece 4 to be formed. Thistool is arranged at an axial distance 16 to the area at which the outerforming tool 2 acts upon the outer contour 10 of the workpiece 4 to beformed. In the shown example, the forming tool is set such that it justcontacts the outer contour 10 in the area of the lowest or least wallthickness in the circumferential direction, i.e., in the shown examplein the area with the wall thickness 8, while it takes off or removes aswarf in the remaining area of the circumference, in the area with thefirst wall thickness 7 a swarf with the thickness 17. This insures thatthe wall thickness of the workpiece is uniform in the area at which theouter forming tool 2 acts upon the outer contour 10 of the workpiece 4to be formed. In one embodiment, one or the other or both of themachining tool 15 and/or the forming tool 2 may be mounted on atranslatable carriage such that the axial distance (16) between theouter forming tool (2) and the machining tool (15) can be adjusted.

When carrying out the method according to the invention, it may beuseful to pre-form or pre-size a certain area of the workpiece 4 to beformed in advance, without the machining tool 15 machining the workpiece4 to be formed as the forming is taking place but rather doing this stepprior to forming the workpiece. In the shown example, this is the axialarea 19 that has an expansion in the axial direction, preferably of atleast 1 and/or at most 10 mm.

Another feature of the present invention is the optional provision of acooling liquid or agent 21 provided by a cooling apparatus 23 comprisinga hose and nozzle connected to a source of cooling liquid, as is wellknown in the art.

Accordingly, the present invention provides a machining tool that isdesigned and placed such that the machining tool can act upon the outercontour of the workpiece at the same time as that of the forming tool inorder to insure that the diameter of the workpiece is uniform before theworkpiece is acted upon by the forming tool, to prevent whip orcurvature in the workpiece.

Modifications and substitutions by one of ordinary skill in the art areconsidered to be within the scope of the present invention, which is notto be limited except by the allowed claims and their legal equivalents.

REFERENCE CHARACTER LIST

-   1 Device-   2 Outer forming tool-   3 Inner forming tool-   4 Workpiece to be formed-   5 Feed direction-   6 Formed workpiece-   7 First wall thickness-   8 Second wall thickness-   9 Center line-   10 Outer contour-   11 Center line-   12 Length-   13 Length-   14 Distance-   15 Machining tool-   16 Axial distance-   17 Swarf Thickness-   19 Axial area-   X Axis of rotation

1. A device (1) for forming a hollow and at least essentiallyrotation-symmetric workpiece (4), the device (1) having an inner formingtool (3) for supporting an inner contour of the workpiece (4) and anouter forming tool (2) for introducing a forming force into an outercontour (10) of the workpiece (4), wherein the workpiece (4) can berotated relative to the outer forming tool (2) around an axis ofrotation (X), characterized in that the device (1) has a machining tool(15) located proximate the workpiece (4) and proximate the outer formingtool (2) and wherein the machining tool (15) is configured such that themachining tool (15) acts upon a predetermined portion of the outercontour (10) of the workpiece (4) prior to said predetermined portion ofthe outer contour (10) being acted upon by said forming tool (2) and atthe same time as the forming tool (2) is acting upon a priorpredetermined portion of the outer contour (10) previously acted upon bysaid machining tool (15).
 2. The device (1) as in claim 1, characterizedin that the forming tool (2) has a forming roll.
 3. The device (1) as inclaim 2, characterized in that the forming tool (2), in particular theforming roll has a surface for transferring the forming forces to theworkpiece (4) and is designed such that the axial movement of theworkpiece (4) causes an increasing displacement of the material of theworkpiece (4) relative to the outer forming tool (2) in the direction ofthe inner forming tool (3).
 4. The device (1) as in claim 1,characterized in that the device (1) has a plurality of outer formingtools (2) preferably arranged opposite relative to the inner formingtool (3).
 5. The device (1) as in claim 1, characterized in that themachining tool (15) acts upon the outer contour (10) of the workpiece(4) by removing swarfs of workpiece material, and wherein the device (1)has a swarf suction device for removing the swarfs arising at themachining tool (15).
 6. The device (1) as in claim 1, characterized inthat the device (1) further includes a cooling apparatus for applying acooling agent in an area of the forming tool (2) and/or of the machiningtool (15) acting upon the workpiece (4).
 7. The device (1) as in claim1, characterized in that an axial distance (16) between the outerforming tool (2) and the machining tool (15) can be adjusted.
 8. Thedevice (1) as in claim 1, characterized in that an effective area of theforming tool (2) is located in an axial direction in an area of an endzone of the inner forming tool (3).
 9. A method for forming a hollow andat least essentially rotation-symmetric workpiece (4), wherein theworkpiece (4) relative to an outer forming tool (2) is put in rotationaround an axis of rotation (X), which at least approximately correspondsto its axis of symmetry, wherein the outer forming tool (2) acts upon anouter contour (10) of the workpiece (4) and through exerting a formingforce onto the outer contour (10) of the workpiece (4) plasticallydeforms the workpiece (4), wherein the workpiece (4) with its innercontour is supported on an inner forming tool (3), wherein the workpiece(4) carries out a feed movement parallel to the axis of rotationrelative to the outer forming tool (2), characterized in that machiningof an area of the outer contour (10) of the workpiece (4) yet to beformed takes place during forming of a prior machined area.
 10. Themethod as in claim 9, characterized in that the superimposition of therotation and the feed movement results in a helical track along whichthe outer forming tool (2) acts upon the workpiece (4).
 11. The methodas in claim 9, characterized in that at least during forming of an axialsection of the workpiece (4), machining occurs with unevenly distributedmaterial removal across the circumference of the outer contour (10)workpiece (4).
 12. The method as in claim 9, characterized in thatmachining eliminates an eccentricity of the outer contour (10) of theworkpiece (4) relative to the axis of rotation (X).
 13. The method as inclaim 9, characterized in that initially an axial area, preferably anend zone of a workpiece is formed using the forming tool such that theformed area with its inner contour comes to rest on the inner formingtool (3) prior to the start of machining.
 14. The method as in claim 13,characterized in that the workpiece (4) is shifted in axial directionbeyond the end zone of the inner forming tool (3) through a feedmovement.
 15. The method as in claim 9, characterized in that the lengthof the workpiece (4) increases in axial direction through the plasticdeformation.
 16. The method as in claim 9, characterized in that a wallthickness (7, 8) of the workpiece (4), a circumference of the outercontour (10) of the workpiece (4) and/or a circumference of the innercontour of the workpiece (4) is reduced through the plastic deformation.17. The method of claim 9 wherein said machining of an area of the outercontour (10) of the workpiece (4) yet to be formed takes place duringforming of a prior machined area is performed by a machining tool (15)that is configured such that the machining tool (15) acts upon apredetermined portion of the outer contour (10) of the workpiece (4)prior to said predetermined portion of the outer contour (10) beingacted upon by said forming tool (2) and at the same time as the formingtool (2) is acting upon a prior predetermined portion of the outercontour (10) previously acted upon by said machining tool (15).